let's go to chris over at the pentagon. >> south korean officials estimate that this explosion could have been as high as 6 to 7 militons. the key thing is whether north korea managed to miniaturize the device, that is make it small enough that one day soon they would be able to marry a nuclear war head on top of a long range missile. >> reporter: on the eve of president obama's address to the american people, north korea sent a message of its own and mumsed its way into the state of union. >> they represent a serious threat to the united states of america. we have got to be prepared to deal with that. >> reporter: north korea detonated an explosion deep under ground. the u.s. military deployed a special plane to japan that collects radioactive particles. but the plume has to extend outside north korean air space before the plane can collect samples. >> we'll find out everything i have got to say tonight. >> reporter: sources say president obama adjusted his speech to mention north korea's nuclear ambitions, but after the u.n. called an emergency meeting, the message is already being